The invention relates to a process of controlling a treating machine which runs back and forth along a flying stock such as rod or sheet material and in which a drive to treat the stock is performed by a numerical control (NC) at the instant a speed synchronization is achieved between the machine and the stock after the latter is allowed to travel through a distance corresponding to a preset length determined for the intended treatment.
Subsequent to the invention disclosed in Japanese Patent No. 898,649, entitled "Digital servo flying cutter", a change was made from a mechanical drive to a numerically controlled drive in that a reciprocatory flying cutter in which a carriage having a cutter mechanism mounted thereon is started in following relationship with a running stock such as slab, rod, tube or the like to move in the same direction as the stock in order to cut the latter on its fly, whereupon the movement of the carriage is reversed to return to its home position. Since then, the disclosed reciprocatory flying cutter has been developed into a variety of forms and manners such as a die set shear including a pair of upper and lower cutting edges which are impacted by a press into meshing engagement, a running cut-off carriage which carries a rotary saw or disk cutter together with a mechanism which presses the saw or cutter against the stock, a running carriage mounting a cutting mechanism which operates as a milling machine. For information of the related art, refer to U.S. Pat. No. 4,099,113 (issued Jul. 4, 1978) and U.S. Pat. No. 4,266,276.
The numerical control is not limited to the field of cutting mechanisms, but is currently finding applications in running carriages on which treating mechanisms of other types are mounted as well. The other applications include, for example, a reciprocatory running treating machine which carries a variety of dies to perform a boring or notching operation on a running molded material or a reciprocatory running treating machine on which a mechanism is mounted which enables the application of a printing, and a heating or an overlay application to a running film, paper or cloth.
As an example of NC drive used with a conventional back-and-forth running machine of the kind described, a cutter is shown in FIG. 1. A running stock 11 passes in rolling contact with a length measuring roll 12, which activates a length encoder 13, which in turn produces a pulse for each given increment of travel of the stock 11. A length counter 14 is cleared at the time the cutting operation is completed, for example, by a signal from a sensor which detects a crank angle corresponding to the completion of the cutting operation in the arrangement of FIG. 1. Accordingly, a count in the length counter 14 indicates a run length L.sub.1 which the stock 11 has run since the time the counter is cleared.
On the other hand, there is provided a back-and-forth running cutter which travels back and forth along the stock 11. Specifically, a cutter holder 15 carries a rack 16 which meshes with a pinion 17, which in turn is coupled through a reduction gear 19 with a motor 18 to be driven for rotation. An encoder 21 is mounted on the end of the motor shaft and produces a pulse, which is fed to length counters 22, 23 to be counted thereby. It is to be noted that the length counter 22 is cleared at the same time as the length counter 14. Accordingly, the length counter 22 indicates a travel length L.sub.2 of the cutter holder 15 from a home position.
A desired cut length L.sub.0 which is loaded in a presetter 24 and the counts L.sub.1, L.sub.2, of the length counters 14, 22 are input to an adder 25, which then delivers a length to go or remaining length E, which is given by L.sub.0 -(L.sub.1 -L.sub.2)=L.sub.0 -L.sub.1 +L.sub.2.
The control aims at reducing the remaining length E to zero, but it is unavoidable that the cutting operation is initiated before E is reduced to zero, and in such instance, the residual deviation e.sub.0 is not discarded, but is incorporated into the next cut length L.sub.0. Thus E=L.sub.0 -L.sub.1 +L.sub.2 +e.sub.0.
The remaining length E is converted into a speed V.sub.B in a numerical speed converter 26 which provides a root function V.sub.B =K .sqroot.E in order to change the speed V.sub.B linearly as the remaining length E is reduced, thus maintaining the acceleration constant. A frequency-to-speed converter 29 converts a pulse frequency from the length encoder 13 into a stock running speed V, from which the speed V.sub.B is subtracted in an adder 31, which thus delivers V.sub.C =V-V.sub.B. As long as a sign decision unit 32 renders a determination of V.sub.C &lt;0 or that the remaining length E is long, a change-over switch 33 controlled by the sign decision unit 32 selects V.sub.D rather than V.sub.C as a speed reference V.sub.RE. Since the length counter 23 is preset by a home sensor 20 to a distance H.sub.L to an actual home, it follows that at the time of completion of the cutting operation which takes place as a result of forward or advancing movement of the cutter holder 15, a count L'.sub.2 in the counter 23 is a high value while an output V.sub.D =-K.sqroot.L'.sub.2 from a numerical speed converter 34 is a negative high value. A root function is used for V.sub.D in the same manner as for V.sub.B in order to change V.sub.D linearly as L'.sub.2 is reduced, thus maintaining the acceleration constant.
The pulse from the encoder 21 is also applied to a frequency-to-speed converter 35, which detects the speed of rotation of the motor 18. An output from the converter 35 is fed as a speed feedback signal to an adder 36, where the speed feedback signal is subtracted from the speed reference V.sub.RE which is fed from the switch 33 through a limiter 27. An output from the adder 36 is used to drive the motor 18 through an amplifier and driver circuit 37. The circuit 37 comprises a thyristor converter when the motor 18 is a d. c. motor, or comprises a PWM vector inverter when the motor is an a. c. motor.
Immediately after the completion of the cutting operation, the remaining length E is long as mentioned previously, and hence V.sub.C &lt;0, and V.sub.D is selected as the speed reference V.sub.RE. V.sub.D assumes a negative high value, and if the switch 33 applies V.sub.D stepwise to the limiter 27, the limitation on the slew rate by the limiter 27 allows V.sub.RE to be changed at a given gradient in order to limit the motor 18 to its allowable torque. Accordingly, the cutter holder 15 is decelerated at a given acceleration and directly moves into the reversing zone. As the home is approached, a deceleration positioning mode is entered and followed by a stop positioning mode with V.sub.0 .apprxeq.0 until V.sub.C is selected by the switch 33.
As the stock 11 continues to run, the length L.sub.1 -L.sub.2 by which the stock 11 leads the cutting edge on the cutter holder 15 approaches the desired length L.sub.0. As V.sub.B =K.sqroot.E is reduced, there occurs a reversal in sign or V.sub.C =V-V.sub.B .gtoreq.0. When this is detected by the sign decision unit 32, the switch 33 changes the selection from V.sub.D to V.sub.C. As V.sub.B decreases linearly, V.sub.C increases linearly, thus producing a linear acceleration. Subsequently an on-the-fly positioning mode is entered in which the running of the stock 11 is tracked in order to maintain V.sub.B .apprxeq.0. At this time, the remaining length E is given as follows: EQU E=L.sub.0 -L.sub.1 +L.sub.2 +e.sub.0 =e'.sub.0
The current residual deviation e'.sub.0 is approximately equal to the previous e.sub.0, and consequently, we have EQU L.sub.0 -L.sub.1 +L.sub.2 .apprxeq.0 or L.sub.0 .apprxeq.L.sub.1 -L.sub.2.
In a press cutting operation as illustrated in FIG. 1, a cutting command is issued prior to the remaining length E approaching zero in anticipation of a mechanical lag in initiating the cutting operation. In response to the command, a clutch 38 is turned on and the torque from a flywheel 39 which is maintained in rotation by a motor 41 is transmitted to a crank mechanism 42 to rotate it, whereupon a press 43 is pressed down toward the bed to allow an upper cutting edge 44, as assisted by a lower cutting edge 45, to cut off the stock 11. In response to a cutting complete signal from a sensor which detects the angle of the crank mechanism 42, the clutch 38 changes from its off condition to starting its operation as a brake. A retract signal is derived from this signal, and serves entering the residual deviation e'.sub.0 of the remaining length E and the desired cut length L.sub.0 and clearing the length counters 14,22. The speed reference is then again switched from V.sub.C to V.sub.D, whereby the cutter holder 15 retracts toward the home position.
While the press with the clutch/brake is illustrated in FIG. 1, a cutter is also available which improves the cutting performance through the numerical control of the motor 41 without using the clutch/brake 38 and the flywheel 39 (see Japanese Registered Utility Model No. 1,725,847). In either instance, a cutter of the kind described will be referred to as "die set shear" herein. By contrast, there are many arrangements in which the entire cutting mechanism is mounted on a carriage, which then operates while running. Such an arrangement will be referred to as "cut-off carriage" herein.
A control circuit formed by hardware is shown in FIG. 1, but it should be noted that the use of a computer for digital processing of the control action up to an amplifier which precedes a drive circuit, representing the power section in the amplifier and drive circuit 37, is increasing recently. In this instance, the function of the circuit arrangement shown in FIG. 1 is achieved by software. Instead of the length measuring roll disposed in rolling contact, it is currently possible to employ a non-contact sensor such as a laser Doppler sensor for obtaining a length measuring pulse.
As mentioned previously, there are back-and-forth running machines of the kind described in various forms and manners, but the numerical control remains basically the same. Accordingly, the speed waveform of the motor 18 is fundamentally as illustrated in FIG. 2A. Specifically, the cutter holder 15 is accelerated at a constant acceleration for a time interval t.sub.1, which represents an advancing positioning mode. The speed and the cut length are settled in an advancing settling time interval t.sub.s, and subsequently ,the stock 11 is cut in a cutting time interval t.sub.c (inclusive of associated time intervals before and after the cutting) while the holder is running at the advancing speed V. Upon completion of the cutting operation, a constant deceleration is applied for a deceleration time interval t.sub.2 to reach a speed of zero, and then a retracting acceleration is applied for a retracting acceleration time interval t.sub.3 for retracting movement. When a retracting speed V.sub.R is reached, the holder is allowed to retract at this speed for a retract running time interval t.sub.4. The holder is then decelerated at a constant rate for a time interval t.sub.5, which represents the deceleration for purpose of retract positioning. After the holder remains at rest for a stop positioning time interval t.sub.6, it again enters the advancing acceleration.
Machine specifications
For more than twenty years since Japanese Patent No. 898,649 which triggered the popular use of numerically controlled back-and-forth running cutters, a major concern with the machine specifications of cutters of that kind has been the capability of how short a cut length can be achieved with what level of stock running speed ( or line speed).
Thus L-V curve shown in FIG. 2B represents one of the important machine specifications. In FIG. 2B, the abscissa represents a cut length L while the ordinate represents a stock speed V which permits a cutting operation. A saturation speed V.sub.MAX which is attained for larger values of L is often dictated, not only by the cutter itself, but by the line specifications across the cutter. Since a design which satisfies an L-V curve required as the specification has a direct bearing on the present invention, a detailed discussion will be given below in terms of numerical examples.
Shortest cut length L.sub.MIN at maximum speed V.sub.MAX
A combination of the machine and the stock determines a cutting interval t.sub.c. This is not always equal to a time interval necessary for the cutting operation, for example, a time interval t.sub.co required from the commencement of the rotary saw to descend, then turning to rise, until it clears the stock.
Where a die set shear is operated to cut at the center of the press, the cutting interval t.sub.c must include a waiting time since the alignment of the center of the cutter holder 15 with the position on the stock which is to be cut must be waited for before initiating the cutting operation. Where a stock which is cut by a milling cut-off carriage must be conveyed to a subsequent delivery point, the cutting interval t.sub.c must include a conveying time which follows the cutting operation.
For purpose of subsequent description, the following discrimination is made:
Type A : a machine having a cutting interval t.sub.c which is equal to the interval t.sub.co required for only the cutting operation, PA1 Type B: a machine having a cutting interval t.sub.c which includes a time interval t.sub.c1 required for positioning before the cutting operation, and PA1 Type C : a machine having a cutting interval t.sub.c which includes a time interval t.sub.c2 required for positioning after the cutting operation.
Numerical examples
An example is given to obtain an L-V curve on the basis a speed waveform shown in FIG. 2C. It is assumed that V.sub.MAX =2.5 m/s, maximum retracting speed V.sub.RMAX of the cutter holder 15=3.0 m/s, acceleration .alpha..sub.m =2.5/0.2=12.5 m/s.sup.2, and t.sub.s =0.1 s. For the sake of simplicity, it is assumed that t.sub.c =0.2 at V.sub.MAX for any of types A, B and C, since the machine design is such that either t.sub.c1 or t.sub.c2 may be equal to zero at V.sub.MAX. Then we have EQU t.sub.1 =t.sub.2 =V.sub.MAX /.alpha..sub.m =2.5/12.5=0.2 s EQU t.sub.3 =t.sub.5 =V.sub.RMAX /.alpha..sub.m =3.0/12.5=0.24 s
Because the cutter holder 15 retracts by the length it advanced, EQU ((t.sub.1 +t.sub.2)/2+t.sub.s +t.sub.c)V.sub.MAX =((t.sub.3 +t.sub.5)/2+t.sub.4)V.sub.RMAX ( 1)
applies. Hence, when choosing t.sub.4 =0.1777 and t.sub.6 =0.1, the period T of the cutting operation is equal to 1.457, and L.sub.MIN =T.times..alpha.V.sub.MAX =3.64 m.
The stock cannot be cut to a length less than L.sub.MIN using V.sub.MAX. With the numerical control that has been used heretofore, for L.sub.0 which is greater than L.sub.MIN, there occurs an increase in t.sub.6 only, and in other respects, the speed waveform remains unchanged.
A shortest cut length L.sub.m at each line speed V is determined. EQU ((t.sub.1 +t.sub.2)/2+t.sub.s +t.sub.c)V=((t.sub.3 +t.sub.5)/2+t.sub.4)V.sub.RMAX ( 2) EQU (t.sub.1 +t.sub.s +t.sub.c +t.sub.2 +t.sub.3 +t.sub.4 +t.sub.5 +t.sub.6)V=L.sub.m ( 3) EQU t.sub.1 =t.sub.2 =V/12.5, t.sub.3 =t.sub.5 =V.sub.RMAX /12.5=0.24(4)
using these equations, when t.sub.4 &lt;0 occurs, the speed waveform is changed to one shown in FIG. 2D where the constant speed retracting interval t.sub.4 is made equal to zero. In this instance, the above equations (2) to (4) are changed as follows EQU ((t.sub.1 +t.sub.2)/2.div.t.sub.s +t.sub.c)V=(t.sub.3 +t.sub.5)V.sub.R /2(5 ) EQU (t.sub.1 +t.sub.s +t.sub.c +t.sub.2 +t.sub.3 +t.sub.5 +t.sub.6)V=L.sub.m( 6 ) EQU t.sub.1 =t.sub.2 =V/12.5, t.sub.3 =t.sub.5 =V.sub.R /12.5 (7)
For type A: using t.sub.s =0.1, t.sub.c =0.2 and t.sub.6 =0.1 as chosen before, specific values of V are substituted into the equations (5) to (7), thus determining values of L.sub.m as indicated below.
______________________________________ V t.sub.1 t.sub.c t.sub.4 V.sub.R t.sub.3 T L.sub.m ______________________________________ 2.5 0.2 0.2 0.177 3.0 0.24 1.457 3.64 2.3 0.184 0.2 0.131 3.0 0.24 1.379 3.17 2.1 0.168 0.2 0.088 3.0 0.24 1.304 2.74 1.9 0.152 0.2 0.046 3.0 0.24 1.23 2.34 1.7 0.136 0.2 0.007 3.0 0.24 1.159 1.97 1.5 0.120 0.2 -- 2.779 0.222 1.084 1.63 1.3 0.104 0.2 -- 2.562 0.205 1.018 1.19 1.1 0.088 0.2 -- 2.310 0.185 0.946 1.04 ______________________________________
For type B: Usually a machine design does not require a waiting interval t.sub.c1 at V.sub.MAX. Conversely, the length from the home position to the position where the cutting position is initiated is determined at V.sub.MAX as follows EQU (t.sub.1 /2+t.sub.s +t.sub.c1)V.sub.MAX =(0.2/2+0.1+0).times.2.5=0.5 m
For V&lt;V.sub.MAX, the presence of t.sub.c1 is necessary to achieve the same value of 0.5 m. Thus from equations given below EQU (t.sub.1 /2+t.sub.s +t.sub.c1)V=0.5 m, t.sub.1 =V/12.5 and t.sub.s =0.1,
t.sub.c1 can be determined, and applying specific values of V while keeping t.sub.6 =0.1 unchanged, L.sub.m is obtained from the period T as indicated below.
______________________________________ V t.sub.1 (t.sub.1 /2 + t.sub.s)V t.sub.c1 t.sub.4 T L.sub.m .DELTA.L.sub.H ______________________________________ 2.5 0.2 0.5 0 0.1767 1.457 3.64 0 2.3 0.184 0.4416 0.0254 0.1505 1.424 3.28 0.0584 2.1 0.168 0.3864 0.0541 0.1227 1.393 2.93 0.136 1.9 0.152 0.3344 0.0712 0.0914 1.347 2.56 0.1656 1.7 0.136 0.2856 0.1261 0.0785 1.357 2.31 0.2144 1.5 0.120 0.24 0.1733 0.0567 1.35 2.03 0.26 1.3 0.104 0.1976 0.2326 0.0359 1.357 1.76 0.3024 1.1 0.088 0.1584 0.3105 0.0161 1.383 1.52 0.3416 ______________________________________
In order to save the waiting time t.sub.c1, the home position may be advanced previously. Denoting the distance from the original home to the advanced home position by .DELTA.L.sub.H, t.sub.c1 can be dispensed with if .DELTA.L.sub.H is chosen as indicated below. EQU .DELTA.L.sub.H =0.5-(t.sub.1 /2+t.sub.s)V
Numerical examples of .DELTA.L.sub.H are listed in the Table given above. Thus, in this instance, while the machine is of type B, the speed waveform becomes the same as for type A as is L.sub.m. In other words, L.sub.m -.DELTA.L.sub.H represents a new version of L.sub.m, which is identical to the L.sub.m for type A.
For type C: A machine design usually does not require the provision of the conveying time t.sub.c2 at V.sub.MAX. Thus EQU (t.sub.1 /2+t.sub.s +t.sub.c)V.sub.MAX =(0.2/2+0.1+0.2).times.2.5=1 m
This means that the print of delivery is located at 1 m from the home position. For V&lt;V.sub.MAX, t.sub.c =t.sub.c0 +t.sub.c2 =0.2+t.sub.c2 are obtained from (t.sub.1 /2+t.sub.s +t.sub.c) V=1, and hence L.sub.m is determined by substituting specific values of V.
______________________________________ V t.sub.1 (t.sub.1 /2 + t.sub.s + t.sub.c0)V t.sub.c2 t.sub.4 T L.sub.m .DELTA.L.sub.H ______________________________________ 2.5 0.2 1.0 0 0.1767 1.457 4.00 0 2.3 0.184 0.9016 0.0428 0.1639 1.412 3.25 0.0984 2.1 0.168 0.8064 0.0922 0.1521 1.368 2.87 0.1936 1.9 0.152 0.7144 0.1503 0.1415 1.326 2.52 0.2856 1.7 0.136 0.6256 0.2202 0.1318 1.284 2.18 0.3744 1.5 0.120 0.54 0.3067 0.1234 1.243 1.86 0.46 1.3 0.104 0.4576 0.4172 0.1159 1.204 1.57 0.5424 1.1 0.088 0.3784 0.5651 0.1095 1.666 1.28 0.6216 ______________________________________
In order to save the conveying time t.sub.c2, the home position may be advanced previously. Denoting the distance from the original home to the advanced home position by .DELTA.L.sub.H, t.sub.c2 can be dispensed with by a choice as given below. EQU .DELTA.L.sub.H =1-(t.sub.1 /2+t.sub.s +t.sub.c0)V
Numerical examples of such .DELTA.L.sub.H are listed in the Table given above. In this instance, while the machine is of the type C, the speed waveform remains the same as for the Type A, as is L.sub.m.
The numerically controlled back-and-forth running cutter has acceleration/deceleration .alpha..sub.m which remains fixed at a value representing a stringent requirement. This causes a high mechanical impact, and a repeated application of the impact has a significant influence upon the machine life. Oscillation caused by the impact acts as an external disturbance, increasing a variation in the cut length. specifically, the choice of the acceleration .alpha..sub.m is made on the basis of the L-V curve which represents the machine specification so as to establish an acceleration which enables a cutting to the shortest cut length L.sub.m including L.sub.MIN on the L-V curve. It will be noted that an operation of the machine with a line speed V less than V.sub.MAX and for a cut length L.sub.0 greater than L.sub.m, or an operation in a region below the L-V curve which is shown hatched in FIG. 2B, merely results in increasing the length of the stop interval t.sub.6 if the conventional numerical control is followed. In practice, however, almost all operations take place, not on the L-V curve, but below it. Various back-and-forth running treating machines referred to above establish an acceleration .alpha..sub.m along the preset treating length L.sub.0 -stock speed V curve, which is the machine specification similar to that of the conventional cutter, and the acceleration/deceleration relative to the working bed is fixed to the .alpha..sub.m thus established, which is seen to be a harsh requirement upon the machine.
It is an object of the invention to provide a process of numerically controlling a back-and-forth running treating machine which allows an alleviation of the acceleration and a reduction in the retracting speed on the basis of the line speed V and the preset length L.sub.0 in a tenable manner for the machine.